Several insect species in the family Curculionidae are commonly referred to as citrus root weevils. In Florida, and throughout the Caribbean region, the West Indian sugarcane borer weevil, Diaprepes abbreviatus L., is the root weevil of greatest economic significance to citrus. The insect was first detected in Florida in 1964, and currently infests an estimated 150,000 of the 845,000 acres of commercial citrus orchards. During the past decade, D. abbreviatus has become the most serious biological threat to the well-being of citriculture in Florida because of its high incidence, its devastating effect on trees, and because cost-effective IPM strategies have been elusive. Prior to 1998, attempts to intervene in the soil-borne phase of the weevil life cycle were hampered by the absence of registered, effective soil-applied pesticides, due to environment concerns. For these reasons, the use of entomopathogenic nematodes to manage citrus root weevils has had a high priority for more than a decade among both researchers and citrus growers in Florida. Adult D. abbreviatus feed and oviposit on the leaves of citrus and alternate host plants in orchards. Newly-hatched (neonate) larvae drop to the soil where they develop for 4–9 months while feeding on the root systems of trees. Pupation occurs in the soil. Young larvae feed initially on the small fibrous roots but as they increase in size they feed on the cortex of more mature, larger roots. The insects create long lesions or channels in the bark of the larger roots, which are then infected by the root-rotting fungi Phytophthora nicotianae Dastur, and P. palmivora (Butler) Butler (McCoy, 1999: Graham & Menge, 1999). The interaction between root weevils and plant pathogenic fungi results in one of the most severe decline syndromes affecting citrus. Trees are sometimes killed by resulting crown rot, but more typically, trees decline rapidly and irreversibly due to cambium girdling and death of large structural roots.
Entomopathogenic nematodes are widely used by Florida citrus growers as an Insect Pest Management tactic for control of citrus root weevils (Diaprepes abbreviatus). Nematodes of the genera Steinernema and Heterorhabditis possess most of the characteristics of an ideal biological control agent for insects [Poiner, Taxonomy and Biology of Steinemematidae and Heterorhabditidae, In Gaugler and Kaya (eds.), Entomopathogenic Nematodes in Biological Control, CRC Press, Boca Raton, Fla., (1990), pages 23–61; and Gaugler, J. Nematol., 13:241–249, (1981)]]. These nematodes search for their insect hosts; they are highly virulent, killing most hosts within 48 hours; they are easily and inexpensively mass produced; they can be conveniently applied in irrigation water; and they have a wide range of insect hosts (Poiner, ibid and Gaugler, ibid). Moreover, the nematodes are a form of biological control, and therefore present fewer issues than do chemical pesticides concerning safety and environmental degradation. The effectiveness of these nematodes is attributed to a mutualistic bacterium of the genus Xenorhabdus associated therewith [Poiner, ibid]. After entry or penetration of the nematode into the insect host, the bacteria are released from the nematode and rapidly multiply, killing the host insect by septicemia. Conversely, the nematodes protect the bacteria from the environment prior to release within a suitable host. However, management of citrus root weevils with nematodes or with chemical measure is relatively inefficient, given the severe level of damage to citrus caused by the weevils. Therefore, improved efficacy of nematodes by virtue of greater virulence or persistence in the soil is desirable. Disclosed herein is a new nematode, which has a demonstrated ability to persist in soil in Florida citrus groves. The virulence of the new nematode in bioassays is superior to that of commercially available nematode species.
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